1. Field of the Invention
The present invention relates to a driver circuit which drives a signal line, a receiver circuit which receives signals transmitted through a signal line, and a signal transmission circuit which includes the driver circuit and the receiver circuit.
2. Description of the Related Art
Recently, a semiconductor integrated circuit has a larger size and faster operating speed. Consequently, it is becoming necessary to drive a long distance signal line with high speed.
FIGS. 1A to 1C each illustrates a construction of a conventional signal transmission circuit. The signal transmission circuit includes a signal line 201, a driver circuit 202, and a receiver circuit 203.
The driver circuit 202 drives the signal line 201 in accordance with a signal input to the signal transmission circuit, and varies voltage potential of the signal line 201. When the variation of the voltage potential of the signal line 201 propagates the end of the potential of the signal line 201, the receiver circuit 203 outputs a signal in accordance with the potential voltage at the end of the signal line 201. When the line distance of the signal line 201 is long and load capacitance related to signal transmission is large, power consumption due to the charging/discharging of the load capacitance becomes large, and signal transmission speed becomes slow because additional time is required for charging/discharging the load capacitance.
In the signal transmission circuit illustrated in FIG. 1B, an input signal is transformed into a signal having a small amplitude by the driver circuit 202, and the signal having the small amplitude is transmitted through the signal line 201. The transmitted signal is recovered to the original amplitude by the receiver circuit 203.
In the signal transmission circuit illustrated in FIG. 1B, amplitude of a signal passing through the signal line 201 is smaller compared to the signal transmission circuit illustrated in FIG. 1A. Therefore, the signal transmission circuit illustrated in FIG. 1B consumes less power than the signal transmission circuit illustrated in FIG. 1A does.
However, because of the small amplitude of the transmitted signal, the signal transmission circuit illustrated in FIG. 1B has low noise resistance. Therefore, it is difficult to reduce the amplitude of the transmitted signal so as to obtain a sufficient power consumption reduction effect.
In the signal transmission circuit illustrated in FIG. 1C, complementary signals in accordance with an input signal are transmitted through a pair of signal lines 201 and 201'. The two signal lines 201 and 201' are disposed adjacent to each other or very close to each other. This makes the noises received by both the signal lines 201 and 201' almost the same, thereby maintaining the potential difference between the complementary signals. Thus, by transmitting the complementary signals using the pair of signal lines 201 and 201', the potential difference between the signal lines 201 and 201' can be transmitted from the driver circuit 202 to the receiver circuit 203 even though the amplitude driving the signal lines is small. This makes it possible to reduce the power consumption required for driving the signal lines.
However, the signal transmission circuit illustrated in FIG. 1C requires two signal lines for the transmission of one signal. This increases the layout area for the signal lines.
Table 1 lists the results of evaluating the signal transmission circuits illustrated in FIGS. 1A to 1C with respect to three aspects, i.e., for power consumption, layout area, and noise resistance. In Table 1, ".smallcircle." indicates that it is superior to other signal transmission circuits and "x" indicates that it is inferior to other signal transmission circuits.
TABLE 1 ______________________________________ Power consumption Layout area Noise resistance ______________________________________ Conventional (FIG. 1A) X .largecircle. .largecircle. Conventional (FIG. 1B) .largecircle. .largecircle. X Conventional (FIG. 1C) .largecircle. X .largecircle. Present invention .largecircle. .largecircle. .largecircle. ______________________________________
As shown in Table 1, a conventional signal transmission circuit cannot simultaneously realize the three characteristics; that is, low power consumption, small layout area, and high noise resistance.